Protein kinases are enzymatic components of the signal transduction pathways which catalyze the transfer of the terminal phosphate from ATP to the hydroxy group of tyrosine, serine and/or threonine residues of proteins. Thus, compounds which inhibit protein kinase functions are valuable tools for assessing the physiological consequences of protein kinase activation. The overexpression or inappropriate expression of normal or mutant protein kinases in mammals has been a topic of extensive study and has been demonstrated to play a significant role in the development of many diseases, including diabetes, angiogenesis, psoriasis, restenosis, ocular diseases, schizophrenia, rheumatoid arthritis, atherosclerosis, cardiovascular disease and cancer. The cardiotonic benefits of kinase inhibition has also been studied. In sum, inhibitors of protein kinases have particular utility in the treatment of human and animal disease.
The receptor tyrosine kinase C-KIT and its ligand Stem Cell Factor (SCF) are essential for hemoatpoiesis, melanogenesis and fertility. SCF acts at multiple levels of the hemoatpoietic hierarchy to promote cell survival, proliferation, differentiation, adhesion and functional activation. It is of particular importance in the mast cell and erythroid lineages, but also acts on multipotential stem and progenitor cells, megakaryocytes, and a subset of lymphoid progenitors (see, Int J Biochem Cell Biol. 1999 October;31(10):1037-51). Sporadic mutations of C-KIT as well as autocrine/paracrine activation mechanisms of the SCF/C-KIT pathway have been implicated in a variety of malignancies. Activation of C-KIT contributes to metastases by enhancing tumor growth and reducing apoptosis. Additionally, C-KIT is frequently mutated and activated in gastrointestinal stromal tumors (GISTs), and ligand-mediated activation of C-KIT is present in some lung cancers (see, Leuk Res. 2004 May;28 Suppl 1:S11-20). The C-KIT receptor also is expressed on more than 10% of blasts in 64% of de novo acute myelogenous leukemias (AMLs) and 95% of relapsed AMLs. C-kit mediates proliferation and anti-apoptotic effects in AML (see, Curr Hematol Rep. 2005 January;4(1):51-8).
C-Kit expression has been documented in a wide variety of human malignancies, including mastocytosis, mast cell leukemia, gastrointestinal stromal tumour, sinonasal natural killer/T-cell lymphoma, seminoma, dysgerminoma, thyroid carcinoma; small-cell lung carcinoma, malignant melanoma, adenoid cystic carcinoma, ovarian carcinoma, acute myelogenous leukemia, anaplastic large cell lymphoma, angiosarcoma, endometrial carcinoma, pediatric T-cell ALL, lymphoma, breast carcinoma and prostate carcinoma. See, Heinrich, Michael C. et al. Review Article: Inhibition of KIT Tyrosine Kinase Activity: A Novel Molecular Approach to the Treatment of KIT-Positive Malignancies. Journal of Clinical Oncology, Vol 20, No 6 (Mar. 15), 2002: pp 1692-1703.